In many aircraft, gas turbine engines perform a number of functions, including providing propulsion for the aircraft and driving various other rotating components such as, for example, generators, compressors, and pumps, to thereby supply electrical and/or pneumatic power. Such engines may be incorporated into auxiliary power units (APU) that supplement main propulsion engines by providing electrical and/or pneumatic power.
A gas turbine engine typically includes a compressor section, a combustion section, and a turbine section. The compressor section compresses air provided at a forward end of the gas turbine engine and provides the compressed air to the combustor section. Fuel is added to the compressed air, and the resulting mixture is ignited within the combustion section to produce combustion gases. The combustion gases are directed to the turbine section, which extracts energy from the combustion gases to provide the motive force necessary to power the compressor section and auxiliary components, such that the gas turbine engine is self-sustaining.
In general, there are a number of ways to start the gas turbine engine, referred to below as “start modes.” In conventional aircraft, the pilot selects the appropriate type of start mode. For example, one such mode is an assisted start mode in which an electric or pneumatic starter motor is used to initially provide a motive force to the shaft connecting the compressor section to the turbine section. The starter motor may be used to increase the speed of the compressor section to a point at which the compressed air provided to the combustion section results in a fuel/air mixture that is suitable for ignition (commonly referred to as “light-off”). Following light-off, the starter motor is discontinued when the gas turbine engine is self-sustaining (i.e., the power generated by the turbine section is sufficient to power the compressor section) such that the gas turbine engine does not require the motive force from the starter motor. In other situations, the start mode may be a windmill start mode in which the air flowing into the engine (as a result of forward motion or forced induction) is used to drive the compressors. As in the assisted start mode, the air flowing into the combustion section is mixed with fuel and ignited. The decision about start mode depends on a number of parameters and either mode may be more appropriate depending on the scenario. Typically, the pilot performs a sequence of steps to select the correct start mode. Inappropriate selection of start mode may result in incomplete and/or delayed starts, and/or excessive engine temperature conditions.
Accordingly, it is desirable to provide engine control systems that start a gas turbine engine in a more automatic and autonomous manner, particularly by providing selection of start mode by the engine control, rather than by the pilot. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.